Strain‐Gauge Rosette Formulae

DURING recent years strain gauges have been used more and more in the aircraft industry as a means of assessing the loads in aircraft structures, both in structural testing laboratories and in flight. This increased use can be mainly attributed to the satisfactory development of successful electrical strain gauges of the resistance type and to the demand by engineers for a more complete knowledge of the load distribution in modern aircraft structures. Electrical strain gauges, although requiring accurate apparatus and a large amount of electrical wiring in addition, are much more easily attached to the structure than mechanical gauges and have the great advantage that they can be mounted in positions inaccessible to most mechanical gauges. This increased use of such gauges has been applied to the determination of the loads in tubes under combined bending and direct loading and to obtaining the direct and shear stresses in sheets and panels. The results of all this has been that more engineers have had reason to use the basic formulae for determining these quantities from the measured strains on three or more gauge lines.